compareTo 比较器

 1 package com.spp.testComparator;
 2 
 3 import java.util.Comparator;
 4 
 5 public class MyComparator implements Comparator {
 6 
 7     @Override
 8     public int compare(Object o1, Object o2) {
 9         if(null==o1||null==o2){
10             return -1;
11         }
12         User u1=(User) o1;
13         User u2=(User) o2;
14         if (u1.getAge() > u2.getAge()) {  
15               return 1; // 第一个大于第二个  
16         } else if (u1.getAge() < u2.getAge()) {  
17               return -1;// 第一个小于第二个  
18         } else {  
19               return 0; // 等于  
20         }
21     }
22 
23 }

　　Test.java:

 1 package com.spp.testComparator;
 2 import java.util.ArrayList;
 3 import java.util.Collections;
 4 import java.util.List;
 5 
 6     public class Test {
 7 
 8         /**
 9          * @param args
10          */
11         public static void main(String[] args) {
12             // 接口比较器比较，是定义在类的外部的，它不会破坏user2本身
13             List list = new ArrayList();
14             User u1 = new User();
15             u1.setName("aaa");
16             u1.setAge(10);
17             list.add(u1);
18             User u2 = new User();
19             u2.setName("bbb");
20             u2.setAge(30);
21             list.add(u2);
22             User u3 = new User();
23             u3.setName("ccc");
24             u3.setAge(20);
25             list.add(u3);
26             //之前：
27             for (int i = 0; i < list.size(); i++) {
28                 User u = (User) list.get(i);
29                 System.out.println("之前："+u.getAge());
30             }
31             
32             Collections.sort(list, new MyComparator());
33             
34             for (int i = 0; i < list.size(); i++) {
35                 User u = (User) list.get(i);
36                 System.out.println("之后："+u.getAge());
37             }
38         }
39 }

 1 package com.spp.testComparator;
 2 
 5 public class User {
 6         public String getName() {
 7             return name;
 8         }
 9         public void setName(String name) {
10             this.name = name;
11         }
12         public int getAge() {
13             return age;
14         }
15         public void setAge(int age) {
16             this.age = age;
17         }
18         private String name;
19         private int age;
20         
21 }

通过实现Comparator接口，可以实现多种复杂情况的比较